The fertilization between plus and minus gametes of Chlamydomonas will be studied in wild-type and non-fusing mutant strains. Three lines of research are proposed. (1) We will re-examine the activation and fusion process by quick-freeze freeze-fracture electron microscopy at room temperature and at cold-inhibitory temperatures, the goal being to document alterations in the membrane that precede and accompany fusion. (2) We will examine the nature of surface material covering the mating structures of this organism by enzymatic, lectin, and immunological probes, the goal being to test our hypothesis that the initial event in gametic cell fusion is a complementary recognition between plus and minus surface components. (3) We will utilize two screening procedures to select for additional non-fusing mutant strains, and we will subject existing mutants to genetic analysis.